# Tag Info

72

In your simulation, the camera (or the viewers perspective) is stationary in what seems like in an altitude of a geostationary orbit. However the ISS is not stationary, it is travelling 7.6 km/s. It completes one orbit in 92 minutes. The ISS orbiting is giving the illusion that the Earth is spinning that fast. Note: The Earth does still spin while the ISS ...

42

Two major problems present themselves right away. As the human body is almost neutrally bouyant with water, one might think that there are no issues with the actual movement in water. But this is only partially true. Directional orientation in the water will be very difficult. On earth, when we swim, not only is our chest slightly more bouyant than our legs,...

32

Tracks are heavy, high-friction, and primarily useful in soft/muddy/slippery terrain where the weight distribution is essential to prevent sinking and slipping. They take much more energy to move than wheels, and while on Earth-bound robots that's not so much of a problem, on a lander this is to be or not to be of the mission. They weigh quite a bit. I can'...

22

As others have noted, the ISS orbits the earth extraordinarily quickly, and that explains the discrepancy. However, there may still be a small error in your simulation. Whether or not there is an error depends on where you intend the "camera" to be. My suspicion is that your simulation was created as follows: Make a sphere at the origin, inclined 23 ...

21

A similar question was asked on the Robotics SE. The Wheels provide a lot of flexibility, like with the rocker bogie system. where the rover can climb over obstacles up to twice the diameter of the wheels And Tracks are usually heavier than wheels. Making it more expensive for deployment . It's also easier to maneuver with wheels than rely on the skid ...

19

From a logistical perspective, solid wheels have a significant benifit over tracks; Maintance. Tracks lower the ground pressure of the vehicle to something on the order of human foot, the trade off for that is two fold. You still have "wheels" inside the track, ususally lots of them, and they each have hubs and bearings and potential places to fail. ...

13

The ISS takes approximately 90 minutes to circle the Earth. This presumably results in the higher apparent speed of rotation.

12

Off the top of my head, two issues for free swimming (no breathing gear) I can think of: Absent a sense of "up" and "down", it would be very easy to become disoriented and lose track of where the nearest surface is to take a breath. Surface tension will become the dominant force governing water flow as you come up for breath. In particular, the water will ...

12

It would stand still, because of the equal and opposite force rule (aka conservation of momentum). On earth's surface it's possible to have a self-propelled butt-kicking machine by having a slow "wind-up" phase alternating with an abrupt "kick". During the wind-up, static friction with a ground surface holds the vehicle in place, but the kick phase can ...

10

Not a good assumption. Curiosity would die a very quick thermal death on the surface of Venus. But to answer your question, Curiosity's MMRTG would work on Venus and provide power. The smaller temperature delta reduces the efficiency of conversion, but its not too bad. See this paper. The atmospheric density and wind are not a factor at all for rover ...

10

You can sort of swim, but it would be very slow. The viscosity of air vs water is very low. Therefore the 'scoop' your hands or feet can get of the fluid, to propel it, and thus move you around would need to be much higher. If you had fans (or 'wings') on your arms you would be more effective. As for the corgi? Not likely, or at least very, very slowly. ...

9

The winds on Mars are much faster than typically on Earth, however, the atmosphere is much thinner. This can cause some unusual effects, somewhat analogous to high speed/ low torque vs low speed/ high torque. Let's assume the satellite dish had a surface area of $1 m^2$, a reasonable assumption. Also, let's use the math from this question, and let's use ...

7

With the exception of the propellant for Zvezda's thrusters, which is fairly simple and fairly short plumbing, you are asking about the Space Station's Environmental Control and Life Support Systems (ECLSS). The plumbing for propulsion is quite simple. This plumbing has existed since the dawn of spaceflight. The plumbing needed for life support is anything ...

7

Why don't they fear those objects will move some switch or unplug some connector? Because none of the crucial switches aboard the station are installed without some sort of a safety mechanism, require multiple different actions to initiate them or aren't as easy to move out of position (such as rotating levers for bulkhead doors - sometimes, they would ...

6

The equation for aerodynamic drag is: $$P_d = \mathbf{F}_d \cdot \mathbf{v} = \tfrac12 \rho v^3 A C_d$$ Curiosity has a max. speed of 5 cm/s (0.18 km/h). Air density $\rho$ of Venus is 67 $kg/m^3$, where on Earth it's 1.2 $kg/m^3$. I'll guesstimate frontal area A = 4 $m^2$ and $C_d$ = 1, then at 5 cm/s the drag force due to the rover's own speed ...

6

I should actually add that there is a possible third option. A 4 or 6 legged walker can probably work well on any terrain. A possible disadvantage is that it could be maintenance heavy.

4

In addition to weight as other people have mentioned, tracked vehicles are extremely maintenance intensive relative to wheeled variants. When the nearest mechanic is hundreds of thousands to tens of millions of miles away, not breaking or wearing out under use is a critical requirement.

4

Another point is that 6 wheeled robots can still move when one or more individual wheels' motors fail (okay not as elegantly), however, a tracked vehicle is doomed at this point.

3

Andy Weir himself considers this the biggest scientific inaccuracy in the movie in an interview with NPR he stated: The biggest inaccuracy in the movie is straight from the book, so it's also a big inaccuracy in the book. It's right at the beginning, the sandstorm that strands him there. (So this is not a spoiler; everyone knows he gets stranded there due ...

3

A person could swim. But that would take many, many effort to generate even a little of velocity. The viscosity of air is much lower than the viscosity of water. When you swim in water you are practically pushing the water away, creating a force that makes you go the direction you're swimming to. Imagine this with air. You could simulate this yourself too: ...

2

The martian winds are not as strong as portrayed in the Martian. The air pressure on Mars is 1% of Earth sea level, and 200kph, while enough to notice, would not be enough to blow you over. Calculating the earth equivalent speed using the formulas in the related question posted by @1337joe 200kph on mars is 25kph on the earth, or 15mph. That's a breeze, not ...

2

Look up "thrown track". Tracked vehicles actually quite often lose one of their tracks, especially when turning. This is a huge issue, for both civilian an military vehicles. With enough manpower, time and winches, they can be re-tracked - on Earth. For a rover, such event would end a mission. For space use, tracks are ridiculously unreliable.

2

To swim in water you need to breathe air with only a small content of water droplets. You need to know when it is possible to open your mouth and take a deep breath of pure air. If you inhale too much and too often water instead of air you are in danger of drowning. In zero gravity and under the influence of swimming, there will be many water droplets ...

2

"lets imagine a ball of water with a 5m radius floating in empty space within a suitably large space station" The sphere of water would break apart from the turbulence caused by the swimmer. Then the swimmer would drown inhaling the floating soup of water fragments. If you enclose the water in a tank, then you can "swim underwater" - but getting in and ...

1

Mixed water and air environments could indeed be quite dangerous in microgravity. But an all-water environment should be possible. For a human to experience sustained microgravity already requires a breathing apparatus; often this is habitat or capsule sized, but personal units exist as well. Several have commented on the challenge of moving between all-...

1

Yes, you can. This subject is well covered in the book The Integral Trees (1984) by Larry Niven The majority of Smoke Ring animals have evolved to fly on at least an occasional basis—even the fish. The Smoke Ring contains numerous "ponds," globs of water of various sizes which float free like everything else. While there are aquatic and amphibious ...

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